October 2015 Gaithersburg 2 WNW Maryland – Summary, analysis for the NJWO Blog

by Kevin Shaw, Observer in charge

Average high temperature 64.8° (- 0.6°) Average low temperature 45.4° (+ 1.5°) Mean temperature 55.1° (+ 0.5°) Precipitation 3.59″ (+ 0.09″) Greatest daily amount (date) 1.70″ (28)
Year to date precipitation 35.69″ (- 1.96″) High temperature for the month (date) 78° (9,22)
Low temperature for the month (date) 31° (19)
Highest barometric pressure (date) 30.55″ (19)
Lowest barometric pressure (date) 29.55″ (13)
Peak wind gust (date/direction): 23 (18/SW)
Heating degree days for the month: 4
Cooling degree days for the month: 311
Greatest diurnal range (date): 33.6° (22)
Least diurnal range (date) 6.2° (1)

Fog days: 4
Thunder days: 1
Sunny/clear days: 15 Partly Cloudy days: 7 Cloudy days: 9

Days with measurable precipitation (=>.01″) = 6
Days with maximum temperatures of 70 or more = 8
Days with minimum temperatures of 32 or less = 2

by Kevin Shaw, observer in charge

October 2015 was quite normal statistically in both temperatures and precipitation. We had the usual below normal high temperatures and above normal minimum temperatures, but this October the numbers were quite small compared with most of the other previous months. Precipitation fell mostly at the beginning and end of the month, with about 90% of the month’s precipitation falling on 4 days: October 1-3 and our wettest day of the month (1.70″) on the 28th. The rainfall on the 28th set a new daily record for precipitation for that date. No other precipitation records were set. The only temperature record that was set was the low maximum temperature recorded on the 18th (50°) which also was the date when a mixed rain and snow shower fell for a short time that afternoon, establishing a record snow for the date (a Trace) and only the third time I have recorded any amount of snowfall in October, with previous October snowfalls occurring back in 1979 and 2011. The first 32° freezing minimum temperature was recorded on the 18th with 32.3°, followed by the month’s coldest reading of 31° on the 19th. This compares very well with my long-term average first freezing temperature of the fall, a 37 year average date of October 21. Fall color was really nice this year and some still remains into mid-November.

The average maximum temperature for the month was 64.8° (- 0.6°), the average minimum temperature was 45.4° (+ 1.5°). The resultant mean average temperature for the month was 55.1° (+ 0.5°). There were no real remarkable temperature trends during the month, just the usual gradual downward trend during the month, with significant ups and downs through out the month.

The month’s total precipitation amount of 3.59″ was 0.09″ above the normal October amount of 4.20″. It was the 16th wettest month in my 37 year period of record (POR). The 6 days of measurable precipitation during the month was below the long term average of 9.6 days. The year to date (YTD) precipitation total of 35.69″ now puts us 1.96″ below the normal YTD average amount for this time of year of 37.65″.

The monthly barometric pressure extremes were a modest 30.55″ on the 19th during our coldest period of the month with the 29.55″ lowest pressure value being recorded on the 13th, during a cold frontal passage period. Average barometric pressure for the month was 30.11″, within .06″ if you averaged the two extreme values (30.55″ and 29.55″). So far with eight months study under my belt, this relationship has shown up as the same in March, 0.06″ difference in April, and 0.02″ in May and June, 0.005″ in July, 0.01″in August, 0.04″ in September, and 0.06″ in October. These values look very promising for developing a strong relationship there. Further study continues through (at least) the rest of the year.

The distribution of 15 sunny, 7 partly cloudy and 9 cloudy days coincided roughly with the slightly above normal monthly precipitation 3.59″ amount.

There were 4 heating degree days and 311 cooling degree days. There were 4 days with fog observed and 1 thunder day. The peak wind gust during October was a modest 23 MPH out of the SW during our most significant cold frontal passage on the morning of the 18th.

My maximum temperature frequencies included 8 days between 70°and 79°, 13 days from 60° to 69°, and 10 days between 50° and 59°, On the minimum temperature frequency side of things, there were 6 days between 30° and 39°, 16 days between 40°-49°, 8 days between 50° and 59° and 1 day with minimums of 60° or greater.

The diurnal range average was a bit below normal (19.4° vs the normal 21.5°). The max daily range of 33.6° occurred on the 22nd during the initial warmup after our coldest temps of the season on the 18th and 19th. The lowest daily temperature range of 6.2° occurred on the 1st during our unsettled, wet period at the beginning of the month. We had a total of 4 days with a diurnal range less than 10° (the first 4 days of the month) while there were 3 days with ranges of 30° or more and 11 additional days with ranges of 20° or more, distributed fairly evenly through the rest of the month.

October 2015 was most remarkable by its lack of remarkableness, so to speak. Quite normal conditions during the month, very seasonable for the Fall time of year, with fall color progression running a bit behind at first due to a warm September, but caught up by the end of the month. It looks like another El Nino winter ahead of us, which could mean just about anything. Other factors are involved that could cause great fluctuations in our winter weather. Stay tuned in a few weeks for the November report, heading into the winter and the holiday season!

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